1. Field of the Invention
The present invention relates to program updates in programmable devices and in particular to a method and associated apparatus for performing program updates in a dual-boot programmable device and for using such a dual-boot capable device.
2. Discussion of Related Art
It is generally known in the art to provide updatable boot instruction sequences for initial loading in a programmable device. As used herein, "programmable device" includes processors, field programmable logic devices, and other programmable electronic devices. Processors are computing devices which execute programmed instructions stored in an associated memory (or internally within a cache memory associated with the processor). A processor fetches and executes boot instruction sequences from a memory device to initialize it's operation for a desired application. Field programmable logic devices (FPLDs) are electronic circuits are devices which contain arrays of boolean logic electronic circuits (typically within a single integrated circuit). The interconnections among the various logic circuits are defined by a programmed sequence loaded into the FPLD from an associated memory device (e.g., boot instructions sequences). Further, as used herein, "boot instruction sequences" is intended to broadly include any programmed information which is a loaded or fetched by a programmable device associated with the boot instruction sequences.
Typically, such boot instruction sequences are stored in a memory associated with the programmable device. For example, in a typical personal computing system, a memory device (e.g., a ROM BIOS chip) stores the initial instructions to be executed by the central processing unit (CPU) of the personal computer. When such a personal computer is reset or initially powered on, the central processing unit fetches boot instructions directly from the ROM memory device. Or, for example, an FPLD in a particular application may initially load its configuration from an associated memory device. The initial configuration defines the Boolean logic functions to be performed by the FPLD in its intended application.
The memory device containing the boot instruction sequence is often updatable in the sense that the instructions (the logic functions) contained therein may be re-programmed with updated instructions. For example in a typical personal computer, the boot instructions are often stored in a flash memory device which may be electronically erased in re programmed by instructions operating in the central processing unit. Or for example, a field programmable logic device may be initially programmed upon reset by information stored in a such a flash or programmable memory device associated with the field programmable logic device or updated by instructions operating in an associated processor.
The memory device containing such boot information (program instructions, programmed logic, etc.) are typically updated by first erasing the contents of the memory device then programming the memory device with the updated boot information. A problem can therefore arise if the update sequence fails in some manner. The memory device in case of such a failure may be left in a state wherein it is unusable. For example, the erasure of the memory device may have completed but the re-programming may have failed or the re-programming may have partially failed. If the boot memory device is left in such an unusable state, the entire application may be shut down (e.g., the computer may fail to run or the circuit in which an FPLD is embedded may fail to operate).
In view of the above discussion, is clear that a need exists for improved methods and associated apparatus for using and updating boot memory devices associated with programmable electronic devices.